The present invention relates to an automatic dishwashing machine, i which the washing liquor is pumped to flow into a water-carrying circuit comprising a distribution valve arranged on the delivery-side section of the liquor circulation pump. In the context of this patent, the term washing liquor is used to indicate both the detergent-containing water solution, which is used to carry out the actual washing, ie. soil removal phases, and the sole water medium used in rinsing phases.
A dishwashing machine of the kind adapted to operate with its rotating spray arms being alternately supplied with liquor, and therefore with a reduced amount of washing liquor and a low energy usage altogether, is known from the European patent publication 237 994, whose owner is currently this same Applicant. Such a result is obtained with the use of a valve that comprises a shutter member and at least a first and a second outlet that are connected to respective conduits provided to supply corresponding rotating spray arms, which are in turn spaced vertically from each other. A calibrated offtake passage connects the delivery of the washing liquor circulation pump with the first outlet of the valve.
The shutter member of the valve:
a) moves by gravity into a stable position adjacent to the first outlet of the distribution valve;
b) is adapted to shut that same first outlet, in a first phase of operation of the pump, under the pushing force exerted by the washing liquor flowing into the second conduit, while however leaving said calibrated offtake passage clear and open;
c) is adapted to be displaced into an unstable position, which is adjacent to said second outlet, during a pre-determined stop period of the pump, owing to the washing liquor flowing backwards along said first conduit
d) is adapted to shut the second outlet of the distribution valve, during a second phase of operation of the pump, which substantially begins when the same first conduit is being emptied.
Thanks to such a kind of construction, the so equipped dishwashing machines have been able to be awarded an xe2x80x9cAxe2x80x9d rating in energy usage, ie. efficiency, in the label introduced in accordance with the appropriate European Union directives, with a corresponding significant success on the marketplace. On the other hand, their actual washing, ie. soil-removal performance, eg. in the case of particularly heavily soiled washload items, may not be so good as the performance generally ensured by conventional machines, ie. machines working with both rotating spray arms operating at the same time. It can in fact be readily appreciated that, for a same length or duration of the phases of the washing cycles, the actual length of the time during which any of the washload items in these machines is sprayed with washing liquor is just a fraction of the actual length of the time during which the washload items in conventional machines, m which both rotating spray arms operate at the same time, are sprayed.
It would on the contrary be desirable, and it is actually a first purpose of the present invention, to provide a dishwashing machine that is capable of being awarded an xe2x80x9cAxe2x80x9d rating on the above mentioned European Union label not only for energy efficiency merits, but also as far as its washing and rinsing performance capabilities are concerned
This and further aims of the present invention are reached in a dishwashing machine which, while maintaining the features according to the afore cited European patent, additionally has the features that are recited in the appended claims.